Field of the Invention
The present invention relates to an image pickup system that detects focused state to a subject by irradiating a field with auxiliary light, an image pickup apparatus and a light emission device that are included in the image pickup system, and a focus detection method in the image pickup system.
Description of the Related Art
Image pickup apparatuses, such as a film camera and an electronic camera, employ LED light irradiation that irradiates a subject with LED light pattern and flash irradiation that irradiates a subject with flash light emitted from a discharge tube of a light emission device as methods for irradiating a subject with auxiliary light at the time of detecting a focused state of the subject. For example, an autofocus device that performs focus detection with auxiliary light from a flash device and focus detection with auxiliary light from an LED, selects a focus detection result that has high reliability, and performs lens drive control is proposed (see Japanese Patent Publication No. 4324318 (JP 4324318 B2)).
Since the irradiation with the auxiliary light from an LED (referred to as “LED auxiliary light”, hereinafter) is pattern irradiation, it is effective to a low-contrast subject, but its irradiation range is restricted. On the other hand, although the irradiation range of the auxiliary light from a flash device (referred to as “flash auxiliary light”, hereafter) is wide and is effective to the autofocus (AF) within a wide area in an image pickup screen, it is not enough effective to a low-contrast subject. Accordingly, the technique disclosed in the above-mentioned publication aims to improve AF accuracy by bringing out the merit of each irradiation method exactly in consideration of the merit and demerit of these irradiation methods.
In light photography (referred to as “flash light photography”, hereafter), an image pickup apparatus may use a photographing method what is called bounce flash photography by which irradiates a ceiling etc. with flash light and irradiates a subject with diffuse reflection from the ceiling etc. With the technique described in the above-mentioned patent publication, when a subject is irradiated with the flash auxiliary light in the setting of the bounce flash photography, there is a possibility that a focusing state is not appropriately detected because the subject is not enough irradiated with the flash auxiliary light. Moreover, when the flash auxiliary light is emitted in the state where there is low chance of the focusing state being detected appropriately, there is a problem of consuming electric power superfluously. Furthermore, it is necessary to wait for recovery of the electrical energy accumulated in a capacitor of an electronic flash device in order to perform the flash light photography as the original purpose after emitting the flash auxiliary light. Accordingly, when a release process is performed during the accumulation of the electrical energy, a release delay occurs.
On the other hand, since a light amount of pattern auxiliary light like LED auxiliary light is smaller than that of the flash auxiliary light in general, an area in which the AF auxiliary light functions effectively is limited to the center area in a photographing area of an image pickup apparatus and to a range of a short distance, and there is a problem that it cannot respond to a wide AF area. Accordingly, if priority is always given to irradiation with the pattern auxiliary light, there is a case where the pattern auxiliary light is insufficient to detect the focusing state. In such a case, irradiation with the flash auxiliary light is needed after irradiation with the pattern auxiliary light as a result, which causes a problem of a release delay.